1. Field of the Invention
The present invention relates to a liquid ejecting device that discharges liquid in the form of fine particles, and to the method of ejecting liquid in the form of fine particles.
2. Description of the Related Art
Nozzles that convert liquid into fine particles are used in various applications. For example, spray-drying methods use nozzles to atomize liquid (e.g. water) that includes solids such as additive agents suspended as micro-particles. The atomized liquid is instantaneously dried in a blast of heat producing solid material.
With these types of applications in mind, the present applicant developed a nozzle 80 to eject liquid as fine particles (see Japanese Patent No. 2797080). As shown in the cross-section of FIG. 14, liquid is supplied to an inclined surface 87 from a supply orifice 85. Liquid supplied to an inclined surface 87 is spread into a thin-film flow 88 by high-speed air that flows along the inclined surface 87. The thin-film flow 88 is accelerated by the air flow and ejected into the ambient (gas) from the upper end of the inclined surface 87 forming micro-droplets 89 of the liquid. With this nozzle 80, liquid can be ejected in the form of extremely small particles.
However, since liquid discharged to the ambient from this type of nozzle 80 results from air flow breaking-up a thin-film flow 88 after it is has been spread-out along an inclined surface 87, it has the drawback that ejected particle size becomes non-uniform when the thickness of the thin-film flow is not constant. Specifically, the probability of the thin-film flow thickness becoming non-uniform increases with the flow length along the inclined surface and with the width of that flow. As the thin-film flow becomes thicker, the size of the particles sprayed-off from the thin-film becomes larger. Accordingly, a non-uniform thin-film flow yields particles of non-uniform diameter, and this has the undesirable effect of requiring additional processing such as a step to sort by particle diameter.
In addition, since the method described above streams high-speed air along a smooth surface to spread-out the supplied liquid, it is necessary to consistently expose the inclined surface to the flow of compressed air. Consequently, this method has the drawback that the inclined surface abrades away as result of this continuous exposure. As abrasion progresses, inclined surface material is lost and eventually the capability to atomize liquid is lost.
Further, the method described above spreads liquid supplied from a liquid-flow channel thinly along a smooth inclined surface, and as a result of this thin-film flow, liquid is sprayed off the end of the smooth inclined surface. However, when viscous or strongly adhering (sticky) liquid is used, liquid in the thin-film flow can become extremely thin in a local area. The locally thinned liquid can dry and congeal on the smooth inclined surface, and accumulation of solids at that point can ultimately result in clogging. In particular, clogging becomes an increasing problem as the width of the liquid spray slit is narrowed. If clogging occurs, the nozzle must be disassembled and cleaned causing unavoidable interruption of operations and lost production time.
Still further, in an annular liquid-spraying nozzle, where the liquid is made to flow as a thin-film on an inclined surface via pressurized gas, size-reduction is problematic from a structural perspective and manufacture is difficult.
Refer to Japanese Patent No. 2797080 (1998).